Electr Eng (2008) 90:209–218 DOI 10.1007/s00202-007-0066-2 ORIGINAL PAPER Air-gap force distribution and vibration pattern of Induction motors under dynamic eccentricity Pedro Vicente Jover Rodríguez · Anouar Belahcen · Antero Arkkio · Antti Laiho · José A. Antonino-Daviu Received: 4 July 2006 / Accepted: 28 March 2007 / Published online: 3 May 2007 © Springer-Verlag 2007 Abstract A method for determining the signatures of dynamic eccentricity in the airgap force distribution and vibration pattern of induction machine is presented. The radial electromagnetic force distribution along the airgap, which is the main source of vibration, is calculated and devel- oped into a double Fourier series in space and time. Finite ele- ment simulations of faulty and healthy machines are performed. They show that the electromagnetic force distri- bution is a sensible parameter to the changes in the machine condition. The computations show the existence of low fre- quency and low order force distributions, which can be used as identifiable signatures of the motor condition by measuring the corresponding low order vibration components. These findings are supported by vibration measurements and modal testing. The low frequency components offer an alternative way to the monitoring of slot passing frequencies, bringing new components that allow to discriminate between dynamic eccentricity and rotor mechanical unbalance. The method also revealed a non linear relationship between loading, stress waves and vibration during dynamic eccentricity. P.V. Jover Rodríguez (B ) · A. Belahcen · A. Arkkio Laboratory of Electromechanics, Department of Electrical Engineering, Helsinki University of Technology, P.O. Box 3000, 02015 Hut, Finland e-mail: vicent@cc.hut.fi A. Laiho VTT Technical Research Centre of Finland, P.O. Box 1000, 02044 VTT, Espoo, Finland e-mail: antti.laiho@vtt.fi J. A. Antonino-Daviu Department of Electrical Engineering, Universidad Politécnica de Valencia, P.O. Box 22012, 46071 Valencia, Spain e-mail: joanda@die.upv.es Keywords Dynamic eccentricity · Vibration · Stress · FEM · Fourier analysis · Induction motor 1 Introduction Condition monitoring of electrical machines is becoming increasingly essential for both industrial and academic sec- tors. It plays a very important role for the safe operation of industrial plants and enables to avoid heavy production losses, whereas the choice of adequate monitoring methods is a challenging task for the academic world. The most used indicators for monitoring electrical machines are currents, temperatures, voltages, chemical debris and vibrations. In many cases, the overall vibration level of the machine is sufficient to diagnose mechanical failures [1, 2]. In contrast, the effect of electrical faults on the vibrations is still under investigation. Airgap eccentricity is one of the main faulty conditions of induction machines. It causes excessive stressing of the machine, increasing bear- ing wear and producing harmful vibrations and noise. In the worst case, it could produce rotor-stator rub, with consequen- tial damage to the stator core and winding. Thus, the online monitoring of rotor eccentricity is highly desirable to prevent serious operational problems. Pöyhönen et al. [3] showed that the electromagnetic force is the most sensitive indicator of airgap eccentricity. The only drawback of this indicator is its low accessibility. Neverthe- less, since vibrations are the consequences of the forces on the machine structure, identifiable signatures should be found in the vibration pattern. Finley et al. [4] compiled a resume table with a comprehensive list of electrically and mechanically induced components in the vibration pattern. Their analysis is based on analytical formulas. The conclusion from this paper is that with solid knowledge of motor fundamental it is possible to ascertain the root cause of a vibration problem. 123